Inductive peaking is a popular way of achieving bandwidth extension in broadband amplifiers. An increase in inductor impedance with frequency can be used to counteract the effects of decreasing gain caused by device parasitics. This helps to maintain constant amplifier gain into high frequencies and to achieve a flat bandwidth with a higher—3dB roll-off point. However, inductive peaking is more effective at high AC current levels, because larger current densities require smaller inductors. Small inductors perform better in high-speed circuits, as they tend to have higher self-resonant frequencies. However, if low power operation is a design goal, the size of peaking inductors has to increase. Currently, spiral inductors are some of the largest on-chip components, and can occupy a disproportionately large share of silicon real estate, which translates into higher cost.
There is a need for a design that provides good inductive peaking while also providing a reduction in the size of the inductor, and that can work effectively in circuits employing low currents.